The YopM protein consists of two amino terminal helices followed by variable numbers of an approximately 20 amino acid leucine-rich repeat (LRR) motif (12-20 LRR among different Yersinia strains), forming a horseshoe-shaped protein. The LRR, which have been implicated in protein-protein interactions, make up most of YopM (FIG. 1).
Besides protein-protein interactions with serum proteins such as α-thrombin and α1-antitrypsin (Hines et al., 2000; Heusipp et al., 2006) and a scaffolding function of YopM with two cytoplasmic kinases, RSK1 and PRK2 (McDonald et al., 2003) the molecular function of YopM during infection is only poorly understood.
The fact that yopM mutants of Y. enterocolitica and Y. pestis cannot establish a systemic infection in infected mice (Trulzsch et al., 2004; Kerschen et al., 2004) indicates that YopM is important for full virulence and resistance to innate immunity during infection (Leung et al., 1990). Interestingly, Kerschen et al. showed that YopM of Y. pestis caused a global depletion of natural killer (NK) cells (Kerschen et al., 2004). In association with this NK cell depletion, the spleen/liver tissues of infected mice and in the same manner the macrophages/NK cells isolated from those tissues showed a decreased expression of several proinflammatory cytokines including TNF-α, IFN-γ, IL-1β, IL-12, IL-15, IL-15Rα and IL-18.
How YopM interferes with the signalling pathways of the proinflammatory cytokines is just speculative and has not been investigated. Specifically, it remains elusive how YopM as a locally delivered, bacterial host-cell-contact dependently translocated protein can have a global effect on the host response (Kerschen et al., 2004).
According to a model of Y. enterocolitica infection, YopM is translocated through the T3SS into the host cell cytoplasm. However, other studies also suggest an additional extracellular role of YopM, like binding to the acute-phase protein α1-antitrypsin, and binding of YopM to serum protein α-thrombin which ist supported by a humoral immune response to YopM after infection of mice (Benner et al., 1999, Heusipp et al., 2006; Huck et al. 1998). Furthermore, an apolar secretion (7%) of YopM during in vitro infection has been described by Cheng and Schneewind (Cheng & Schneewind, 2000).
Patent Application having publication number WO2009/115531 reports an additional delivery function of YopM which is independent from the direct delivery of the effector protein by T3SS into the cytoplasm of host cells. In particular, WO2009/115531 discloses Yersinia outer protein M (YopM), a YopM fragment or a YopM variant which are capable of auto penetrating the cell membrane and integrating into the cell cytosol without the requirement of additional factors. The use of this function for delivering a cargo molecule across the membrane to the cytosol of a cell is described therein. WO2009/115531 further discloses that once YopM is integrated into the cell cytosol, YopM is capable of effectively downregulating cytokines, in particularly pro-inflammatory cytokines.
Psoriasis is one of the most common immune-mediated chronic inflammatory skin disorders affecting approximately 2-3% of the population. It is considered as an incurable, life-long skin condition that affects all races, age groups and both sexes. The pathogenesis of psoriasis is complex and not clearly understood. Ongoing research indicates that immune T-cells appear to play a dominant role for the development of this disease. These cells release TNF-α, IFN-α and other pro-inflammatory cytokines that lead to vasodilation, leukocyte migration, and activation of keratinocytes. This further activates dendritic cells which in turn leads to inflammation.
Psoriasis appears in a variety of forms with distinct characteristics. Typically, an individual has only one type of psoriasis at a time.
Plaque psoriasis (psoriasis vulgaris) is the most prevalent form of the disease. About 80 percent of those who have psoriasis have this type. It is characterized by raised, inflamed, red lesions covered by a silvery white scale. It is typically found on the elbows, knees, scalp and lower back.
Guttate psoriasis is a form of psoriasis that often starts in childhood or young adulthood. This form of psoriasis appears as small, red, individual spots on the skin. Guttate lesions usually appear on the trunk and limbs. These spots are not usually as thick as plaque lesions.
Guttate psoriasis often comes on quite suddenly. A variety of conditions can bring on an attack of guttate psoriasis, including upper respiratory infections, streptococcal throat infections (strep throat), tonsillitis, stress and injury to the skin.
Inverse psoriasis is found in the armpits, groin, under the breasts, and in other skin folds around the genitals and the buttocks. This type of psoriasis appears as bright-red lesions that are smooth and shiny. Inverse psoriasis is subject to irritation from rubbing and sweating because of its location in skin folds and tender areas. It can be more troublesome in overweight people and those with deep skin folds.
Primarily seen in adults, pustular psoriasis is characterized by white blisters of noninfectious pus (consisting of white blood cells) surrounded by red skin. It may be localized to certain areas of the body, such as the hands and feet, or covering most of the body. It begins with the reddening of the skin followed by formation of pustules and scaling.
Erythrodermic psoriasis is a particularly inflammatory form of psoriasis that affects most of the body surface. The reddening and shedding of the skin are often accompanied by severe itching and pain, heart rate increase, and fluctuating body temperature.
Erythrodermic psoriasis causes protein and fluid loss that can lead to severe illness. The condition may also bring on infection, pneumonia and congestive heart failure.
Several drugs have been used in the treatment of psoriasis. The four most commonly prescribed systemic medications to treat psoriasis are Methotrexate, Ciclosporin, Acitretin and Hydroxycarbamide. Methotrexate, Ciclosporin and Hydroxycarbamide all work by suppressing the immune system, whereas Acitretin is a Vitamin A derived treatment.
A common disadvantage (besides their side effects) of all drugs currently available for treating this primarily cutaneous disease is that they are only effective when given systemically but are largely ineffective when applied topically because of poor absorption.
Systemic medications are prescription medications that affect the entire body. The systemic treatments that are available to treat psoriasis and psoriatic arthritis are associated with significant short- and long-term side effects. The benefits of psoriasis clearance or improvement must be balanced against the risk of these side effects.
There is therefore the need of an effective therapeutic agent useful in the prevention and/or treatment of psoriasis having a good patient compliance and reduced side effects.
It must be noted that as used herein, the singular forms “a”, “an”, and “the”, include plural references unless the context clearly indicates otherwise. Thus, for example, reference to “a reagent” includes one or more of such different reagents and reference to “the method” includes reference to equivalent steps and methods known to those of ordinary skill in the art that could be modified or substituted for the methods described herein. Unless otherwise indicated, the term “at least” preceding a series of elements is to be understood to refer to every element in the series. At least one includes for example, one, two, three, four, or five or even more. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the present invention. Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.
Several documents are cited throughout the text of this specification. Each of the documents cited herein (including all patents, patent applications, scientific publications, manufacturer's specifications, instructions, etc.), whether supra or infra, are hereby incorporated by reference in their entirety. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention.